This program focusses on the study in cell culture of genetic variation at the locus responsible for expression of the human enzyme galctose-1-phosphate uridylyltransferase (GALT). Both SV40 transformed skin fibroblast and EB transformed lymphocyte lines will be used from normals and galactosemic individuals. Cell clones with revertant GALT activity will be selected in medium containing galactose as the hexose source. Both spontaneous and mutagen-induced clones will be isolated. Emphasis will be placed on the characterization of the structural and functional properties of the GALT enzyme proteins in the various cell clones. Immunological methods will be heavily employed in these studies.